Typed Utilities

Typed utilities are bundled in a single is namespace export. Every check is a method on is, so a single import gives you complete type-guard coverage with excellent TypeScript narrowing.

import { is } from '@vielzeug/toolkit';

📚 Quick Reference

Problem

Implement 📚 quick reference in a production-friendly way with @vielzeug/toolkit while keeping setup and cleanup explicit.

Runnable Example

The snippet below is copy-paste runnable in a TypeScript project with @vielzeug/toolkit installed.

Type Guards

Method	Description
is.string(v)	Check if a value is a string.
is.number(v)	Check if a value is a number.
is.boolean(v)	Check if a value is a boolean.
is.array(v)	Check if a value is an array.
is.object(v)	Check if a value is a plain object.
is.fn(v)	Check if a value is a function.
is.defined(v)	Check if a value is neither null nor undefined.
is.nil(v)	Check if a value is null or undefined.
is.empty(v)	Check if a value is an empty string, array, or object.
is.date(v)	Check if a value is a Date instance.
is.regex(v)	Check if a value is a RegExp instance.
is.promise(v)	Check if a value is a Promise.
is.primitive(v)	Check if a value is a primitive (string, number, boolean, etc.).
is.typeOf(v, t)	Check the typeof a value against a string tag.

Value Checks

Method	Description
is.equal(a, b)	Deep equality comparison between two values.
is.match(v, p)	Check if an object matches a partial pattern or regex.
is.within(v, r)	Check if a number is within a given range.
is.even(v)	Check if a number is even.
is.odd(v)	Check if a number is odd.
is.zero(v)	Check if a value is 0.
is.positive(v)	Check if a number is positive.
is.negative(v)	Check if a number is negative.

Comparison Helpers

Method	Description
is.gt(a, b)	Greater than (a > b).
is.ge(a, b)	Greater than or equal (a >= b).
is.lt(a, b)	Less than (a < b).
is.le(a, b)	Less than or equal (a <= b).

💡 Practical Examples

Robust Type Checking

import { is } from '@vielzeug/toolkit';

function process(data: unknown) {
  if (is.string(data)) {
    // data is narrowed to string
    return data.toUpperCase();
  }

  if (is.array(data)) {
    // data is narrowed to any[]
    return data.length;
  }

  if (is.nil(data)) {
    return 'N/A';
  }
}

Deep Equality & Pattern Matching

import { is } from '@vielzeug/toolkit';

const user = { id: 1, name: 'Alice', settings: { theme: 'dark' } };

// Deep equality
is.equal(user, { id: 1, name: 'Alice', settings: { theme: 'dark' } }); // true

// Partial pattern match
is.match(user, { settings: { theme: 'dark' } }); // true
is.match(user, { name: /^A/ }); // true (regex support)

Comparison Helpers

import { is } from '@vielzeug/toolkit';

is.gt(5, 3); // true  (5 > 3)
is.ge(5, 5); // true  (5 >= 5)
is.lt(2, 10); // true  (2 < 10)
is.le(4, 4); // true  (4 <= 4)
is.within(7, [1, 10]); // true

Numeric Checks

import { is } from '@vielzeug/toolkit';

is.even(4); // true
is.odd(7); // true
is.positive(1); // true
is.negative(-3); // true
is.zero(0); // true

🔗 All Typed Utilities

• is
• is.array
• is.boolean
• is.date
• is.defined
• is.empty
• is.equal
• is.even
• is.fn
• is.match
• is.negative
• is.nil
• is.number
• is.object
• is.odd
• is.positive
• is.primitive
• is.promise
• is.regex
• is.string
• is.within
• is.zero
• is.typeOf

Expected Output

• The example runs without type errors in a standard TypeScript setup.
• The main flow produces the behavior described in the recipe title.

Common Pitfalls

• Forgetting cleanup/dispose calls can leak listeners or stale state.
• Skipping explicit typing can hide integration issues until runtime.
• Not handling error branches makes examples harder to adapt safely.

Related Recipes

• Array Examples
• Async Examples
• Date Examples